int led13 = 13;
bool ledstate = true;
void setup() {
  // put your setup code here, to run once:
  pinMode(led13,OUTPUT);
}

void loop() {
  // put your main code here, to run repeatedly:
  if(ledstate == true){
    for(int i = 0; i < 3;i++){
      digitalWrite(led13,HIGH);
      delay(1000);
      digitalWrite(led13,LOW); 
      delay(3000); 
    }
    ledstate = false;
  }
}
